A router is a network device having software and hardware directed to the tasks of receiving network packets and forwarding the network packets to a destination that brings them closer to their specified destinations. Routers often connect two or more subnets within a network. In wide area networks, border routers may connect two or more autonomous systems.
Most routers, in addition to forwarding network packets, are also configured to communicate directly with their neighboring routers. Such communication often includes the exchange of routing information. For example, if a router acquires or loses one or more serviceable destinations, the router may advertise this change of status to its neighboring routers to allow them to change their routing tables accordingly. In many cases, the router will use a simple update message according to a standard routing protocol (e.g., BGP, OSPF, or ISIS) to communicate this information.
Throughout the drawings, identical reference numbers designate similar, but not necessarily identical, elements.